Size and scaleSpec 4.2.1
Each level of organisation is bigger than the one before. A tissue is many cells, an organ is many tissues, and an organ system is several organs.
Most cells are only tens of micrometres (µm) across, so you need a microscope to see them. Tissues and organs are large enough to see with the naked eye, and are measured in millimetres (mm) or centimetres (cm).
To compare sizes you must use the same unit for both. To change mm to µm, multiply by 1000.
How many cells fit across a tissue?
A strip of tissue is 2 mm wide. Each cell is 40 µm wide. How many cells fit across the strip?
- Convert 2 mm to µm: 2 × 1000 = 2000 µm.
- Divide the width of the tissue by the width of one cell: 2000 ÷ 40.
Answer: 50 cells
Quick check
What is a tissue?
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A group of cells with a similar structure and function.
Why is the stomach an organ?
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It is made of several tissues that work together to perform a specific function.
Put these in order from smallest to largest: organ, cell, organ system, tissue.
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Cell, tissue, organ, organ system.
How many micrometres are in 1 mm?
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1000 µm.